Over the course of the last twenty (20) years it has been debated whether the release of chlofluorocarbons into the atmosphere has effected the stratospheric ozone layer. As a result of this debate and international treaties, the refrigeration and air-conditioning industries have been weaning themselves from the use and production of certain chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Presently, the industries are transitioning towards the use of hydrofluorocarbons (HFCs) having zero ozone depletion potential. Notably, this transition to HFCs necessitated the advent of a new class of lubricants because of the immiscibility of conventional lubricants, such as mineral oil, poly α-olefin and alkylbenzene with HFC refrigerants.
The new class of lubricants includes polyalkylene glycols (PAGs) and polyol esters (POEs) lubricants. While the PAG and POE lubricants have suitable lubricant properties, they are extremely hygroscopic and can absorb several thousand ppm (parts per million) of water on exposure to moist air. This absorbed water leads to undesirable formation of acids that cause corrosion of the refrigeration system and formation of intractable sludges. In comparison, conventional refrigeration lubricants are considerably less hygroscopic and have low solubility, less than 100 ppm for water. Further, PAGs and POEs are considerably more expensive than conventional refrigeration lubricants—typically on the order of three to six times more. PAGs and POEs have also been found to have unfavorable electrical insulating properties.
Accordingly, there existed a need and an opportunity to resolve this solubility problem so that the refrigeration industry could utilize the conventional non-polar mineral oil and alkylbenzene lubricants with polar HFC-based refrigerants. Another need and opportunity also existed when the industry began transitioning towards the use of HCFC-based refrigerants as a replacement for pure CFC refrigerants. This need became apparent due to the diminished solubility of HCFCs in mineral oil, which forced the industry to incurr an additional expense of changing the lubricant to an alkylbenzene to achieve adequate lubricating and cooling performance.
For the last ten years the refrigeration and air-conditioning industries have been struggling with these long-felt but unsolved needs, finally, the present invention satisfies the pressing needs of these industries. While numerous attempts have been made to use conventional non-polar lubricants with polar hydrofluorocarbon refrigerants, the lack of solubility of the polar refrigerant in the non-polar conventional lubricant generally results in a highly viscous lubricant in the non-compressor zones, which unfortunately results in insufficient lubricant return to the compressor. When the non-polar conventional lubricant and the polar refrigerant naturally escape the compressor and enter the non-compressor zones, phase separation/insolubilty of the lubricant and the refrigerant occurs. This phase separation contributes to the highly viscous lubricant remaining in the non-compressor zone, whilst the refrigerant continues its path throughout the refrigeration system. The insolubility and highly viscous nature of the lubricant leaves the lubricant stranded in the non-compressor zones, which leads to an undesirable accumulation of lubricant in the non-compressor zones. This accumulation of lubricant and the lack of return of the lubricant to the compressor zone eventually starves the compressor of lubricant and results in the compressor overheating and seizing. Such stranded lubricant may also decrease the efficiency of the refrigeration system by interfering with heat transfer, due to thick lubricant films deposited on interior surfaces of the heat exchangers (e.g. condensor and evaporator). Further, during cold compressor starts, insoluble refrigerant and lubricant may cause compressor seizure due to poor lubrication and foaming of the lubricant.
For the foregoing reasons, there is a well-recognized need in the refrigeration and air-conditioning industries for a compatabilizer that compatibilizes a polar halogenated hydrocarbon and a non-polar conventional lubricant in a compression refrigeration system, and promotes efficient return of lubricant to the compressor.